Thermistor Resolution

Steinhart-Hart Thermistor Calculator

Answer: infinite

A thermistor has an 'analog' continuous response; a change in resistance (positive or negative thermal co-efficient) in response to a change in temperature. With continuous, analog change, it infinitely resolves any temperature change with a resistance change.

What you read the output of the wheatstone bridge (or the resistance of the thermistor) with determines 'resolution'. And that resolution is associated with a corresponding precision and an uncertainty.

> resolution 0.5%

percent of ? ? ?

Thanks for your input. I had plotted the graph Vout versus Temperature. The characteristic of the graph seems is pretty much linear with only 1.3% of non-linearity error.

Now the last step is to consider the effect of self-heating and suggest a solution to overcome it - i.e. power dissipation in the thermistor will heat up, raise its temperature. I will need to reduce the output (or power supply) of the bridge and use an amplifier. Under what kind of scenario that we may neglect the effect of thermistor self-heating?

A thermistor's dR/dT varies monotonically and smoothly. There is no hysteresis involved.

If your circuit output is to establish a temperature trip point, accuracy is not an issue. If you are measuring temperature you have to compensate for the nonlinearity of all thermistors to get best accuracy. The accuracy, correspondance between temperature and readout, depends on your calibration of the circuit using the particular thermistor.

You can probably come up with an analog scheme to gain accuracy ( null out nonlinearity ) but if you convert the signal to digital you can programmably apply correction terms from your calibration.

Self heating should not be more than a few milliwatts and easily calibrated for.

You may ignore self-heating of the thermistor when its resistance value is tiny with respect to whatever resistance is in series with it, but good luck making a meaningful measurement that way.

I think what you are referring to is the Hysterisis Loop and the accuracy